Experimental design applied to the analysis of volatile compounds in apple juice by headspace solid-phase microextraction

A simple and fast method based on solid-phase microextraction (SPME) followed by fast gas chromatography (Fast GC) has been developed for the analysis of volatile compounds in Asturian apple juices employed in the cider production. Three different fiber coatings have been checked (PDMS, PDMS-DVB and CAR-PDMS) and PDMS-DVB has been presented to be the most suitable one. Experimental design has been employed in the optimization of extraction factors and robustness assessment. The use of Fast GC allowed the separation of 14 compounds (esters, aldehydes and alcohols) in approximately 4 min, clearly reducing the analysis time when compared to conventional GC. Good linearity, recoveries and repeatability of the solid-phase microextraction were obtained with r(2) values, recoveries and relative standard deviations ranging from 0.9822 to 0.9998, 83.2 to 109.8% and 0.5 to 11.7%, respectively, using standard solution.     

Use of headspace capillary GC to study the development of volatile compounds in fresh fruit

The composition of volatile compounds produced by fruit during growth and post-harvest storage and ripening has been studied and the different headspace methods compared. Static and dynamic headspace sampling have been compared and evaluated according to their capacity to collect and concentrate volatiles from the atmosphere surrounding the fruits, and FID, MSD, and organoleptic detection have been compared. The results emphasize that the headspace sampling procedure selected is crucial to the performance of subsequent analysis.     

The performance of various capillary columns for the analysis of volatile flavor compounds in dairy products by dynamic headspace gas chromatography

The aim of this study was to test the suitability and performance of various stationary phases and column dimensions for dynamic headspace gas chromatography of food aromas. The trials were performed using an aqueous test mixture containing thirty seven volatile flavor components of intense aroma, and a sample of ripe Swiss Emmental cheese. The best performance with both samples was obtained with a capillary column coated with a thick film of polydimethylsiloxane. This column resolved the greatest number of compounds in the cheese sample and resulted in the overlapping of one pair of peaks only from the test mixture. Because of its other advantages, i. e. high capacity owing to its film thickness, and insensitivity to the high moisture content of some samples or traces of oxygen in the carrier gas, the polydimethylsiloxane column appears suitable for the analysis of the volatile and highly polar compounds present in complex mixtures such as food aroma.     

Determination of residual solvent in pharmaceutical preparations by static headspace GC

Static headspace GC, a simple, clean technique which is easily automated, appears to be a good approach to the determination of solvent residues in pharmaceutical preparations. The feasibility of this approach has been studied with an automated system. Data is presented for the solvents designated as impurities in pharmaceutical preparations by the United States Pharmacopeia. It was found that the static headspace technique meets the United States Pharmacopeia criteria for sensitivity. The absolute area count precision was <5% relative standard deviation and correlation coefficients to a linear response were >0.999. It was concluded that the technique is viable for this application.     

Optimization of dynamic headspace sampling for the analysis of trace volatile components of grape juice: Use of a PTV injector for intermediate trapping

The use of a programmed temperature vaporizing (PTV) injector has been evaluated for the on-line concentration and injection of trace organic compounds either sampled from the head-space above grape juices or purged from solution. The Simplex method was used to improve the sensitivity of the method by optimization of the experimental conditions.     

Full-range analysis of ambient volatile organic compounds by a new trapping method and gas chromatography/mass spectrometry

This study investigated the feasibility of analyzing a full range of ambient volatile organic compounds (VOCs) from C(3) to C(12) using gas chromatograph mass spectrometry (GC/MS) coupled with thermal desorption. Two columns were used: a PLOT column separated compounds lighter than C(6) and a DB-1 column separated C(6)-C(12) compounds. An innovative heart-cut technique based on the Deans switch was configured to combine the two column outflows at the ends of the columns before entering the MS. To prevent the resolved peaks from re-converging after combining, two techniques were attempted (hold-up vs. back-flush) to achieve the intended "delayed" elution of heavier components. Thus, the resulting chromatogram covering the full range of VOCs is a combination of two separate elutions, with the heavier section following the lighter section. With the hold-up method, band-broadening inevitably occurred for the delayed C(6)-C(7) DB-1 compounds while the light compounds eluted from the PLOT column. This broadening problem resulted in peak tailing that was largely alleviated by adding a re-focusing stage while the DB-1 compounds were back-flushed, and this modified technique is referred to as the back-flush method. With this modification, the separation of the C(6)-C(7) compounds improved dramatically, as revealed by the decrease in peak asymmetry (As) and increase in resolution. Linearity and precision for these peaks also improved, yielding R(2) and RSD values better than 0.9990 and 2.8%, respectively.     

Sampling and gas chromatographic analysis of volatile organic compounds in hot and extremely humid emissions

Adsorptive enrichment on hydrophobic adsorbents, thermal desorption, and capillary gas-chromatographic analysis have been used to determine volatile organic compounds in extremely humid stack-gas emissions from the residential burning of brown-coal briquets. One hundred and fifty two compounds were identified and quantified. Quantitative emission factors were determined for the identified individual compounds in relation to the amount of the fuel used. These factors enable a first assessment of the pollution of the city of Leipzig with volatile organic compounds resulting from the burning of indigenous lignite.     

Optimizing the gas chromatographic separation and detection of polychlorinated biphenyls by use of electronic pressure programming and experimental design

The applicability of electronic pressure control and Taguchi L₂₇ experimental design to the optimization of the gas chromatographic separation and detection of polychlorinated biphenyls has been evaluated. The influence of several experimental variables, column temperature program, carrier gas pressure program, on-column injector temperature program, and make-up gas pressure program, was studied using analysis of variance. Simultaneous optimization of sample introduction, column efficiency, and detector performance could be achieved without compromising system performance. The relationships between system performance and experimental variables were established using regression analysis. Agreement between the simulated and experimental results obtained using suggested optimum conditions demonstrated the applicability of the technique developed in this study. The improvement achieved in the chromatographic separation of PCBs is presented.     

Identification of volatile (micro) biological compounds from household waste and building materials by thermal desorption–capillary gas chromatography–mass spectroscopy

Volatile compounds from biodegradable household waste and infected building materials have been studied by dynamic or equilibrium headspace sampling and concentration on Tenax TA followed by thermal desorption and HRGC-MS. Equilibrium headspace sampling was also used to study vegetables stored for 14–18 days at ambient temperature. Over 200 compounds were tentatively identified. The concentration of organic sulfur compounds from garden waste was high enough to contribute to respiratory problems of waste handling personnel. Nitriles, alkyl nitro compounds, and alkyl nitrates were isolated from radish and carrot samples at low concentrations (10–50 ppb). Air monitoring in waste handling working environments may be required to ensure the safety of personnel. Branched aliphatic aldehydes, carboxylic acids, esters, and 2-alkanones were found in the headspace of the infected building materials, indicating that volatile compounds may be useful for detection of microbial growth in buildings.     

Detection of volatile organic sulfur compounds in water by headspace gas chromatography and membrane inlet mass spectrometry

Two gas chromatographic methods, GC-FID (flame ionization detection) and GC-ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl-methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC-ELCD method and four decades with the GC-FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC-ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods are compared.     

Evaluation of solid-phase micro-extraction coupled to gas chromatography-mass spectrometry for the headspace analysis of volatile compounds in cocoa products

The aroma profile of cocoa products was investigated by headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC–MS). SPME fibers coated with 100 μm polydimethylsiloxane coating (PDMS), 65 μm polydimethylsiloxane/divinylbenzene coating (PDMS-DVB), 75 μm carboxen/polydimethylsiloxane coating (CAR-PDMS) and 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane on a StableFlex fiber (DVB/CAR-PDMS) were evaluated. Several extraction times and temperature conditions were also tested to achieve optimum recovery. Suspensions of the samples in distilled water or in brine (25% NaCl in distilled water) were investigated to examine their effect on the composition of the headspace. The SPME fiber coated with 50/30 μm DVB/CAR-PDMS afforded the highest extraction efficiency, particularly when the samples were extracted at 60 °C for 15 min under dry conditions with toluene as an internal standard. Forty-five compounds were extracted and tentatively identified, most of which have previously been reported as odor-active compounds. The method developed allows sensitive and representative analysis of cocoa products with high reproducibility. Further research is ongoing to study chocolate making processes using this method for the quantitative analysis of volatile compounds contributing to the flavor/odor profile.     

Separation and identification of volatile and non-volatile compounds of wine by sorbent extraction and capillary gas chromatography

Sorbent extraction technology was used to separate the volatile and non-volatile components of wine. The extracts were analyzed by capillary gas chromatography.     

Composition of the basic fraction of marijuana and tobacco condensates: A comparative study by capillary GC/MS

Summary Combined capillary gas chromatography/mass spectrometry has been used to characterize the basic fraction of Mexican marijuana and standard tobacco smoke condensates. A thermostable Superox-coated glass capillary column permitted elution of relatively large nitrogen-containing compounds. Substantial qualitative and quantitative differences between the two materials were noted.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

Focused cryogenic trapping for dynamic headspace and pyrolytic analysis of polymers on a fused silica capillary column

Focused cryogenic trapping has been used to maximize the high resolution capabilities of fused silica capillary columns during dynamic headspace and pyrolytic polymer analyses. Mass spectrometric detection with data system recording/processing provide sensitive, selective, and rapid results. The techniques described herein demonstrate the power of both dynamic headspace and pyrolytic analyses for troubleshooting applications with complex industrial polymer products.     

Experimental design optimization of the analysis of gasoline by capillary gas chromatography

An optimization procedure for multi-step temperature programmed capillary GC was investigated for the detailed hydrocarbon analysis of gasoline. A set of twelve responses, represented by the value of the resolution of the most difficult separations, was selected from several isothermal analyses. The variation of these responses versus the temperature programming conditions was then modeled using a Doehlert matrix for experimental design. Optimal experimental conditions for the twelve responses were then obtained from a response surface optimization. The predicted and experimental resolutions were in good agreement.     

Analysis of volatile compounds emitted from fresh Syringa oblata flowers in different florescence by headspace solid-phase microextraction-gas chromatography-mass spectrometry

In this study, a simple and solvent-free method was developed for determination of the volatile compounds from fresh flowers of Syringa oblata using headspace solid-phase microextraction and gas chromatography-mass spectrometry. The SPME parameters were studied, the optimum conditions of a 65 μm polydimethylsiloxan/divinylbenezene (PDMS/DVB), extraction temperature of 25 °C and extraction time of 30 min were obtained and applied to extraction of the volatile compounds emitted from fresh flowers of S. oblata. The volatile compounds released from fresh flowers of S. oblata were separated and identified by GC-MS. Lilac aldehyde A, lilac aldehyde B, lilac aldehyde C, lilac aldehyde D, lilac alcohol A, lilac alcohol B, lilac alcohol C, lilac alcohol D, α-pinene, sabinene, β-pinene, myrcene, d-limonene, eucalyptol, cis-ocimene, benzaldehyde, terpinolene, linalool, benzene acetaldehyde, α-terpineol, p-methoxyanisole, p-anisaldehyde, (Z,E)-α-farnesene and (E,E)-α-farnesene were the most abundant volatiles released from fresh flowers of S. oblata var. alba. The relative contents of main volatile fragrance were found to be different in emissions from two varieties of S. oblata flowers (white or purple in color). The four isomers of lilac alcohol and four isomer lilac aldehyde were the characteristic components of the scent of fresh flowers of S. oblata. The main volatile fragrance from fresh flowers of S. oblata var. alba in different florescence ((A) flower buds; (B) at the early stage of flower blooming; (C) during the flower blooming; (D) at the end of flower blooming; (E) senescence) were studied in this paper. The results demonstrated that headspace SPME-GC-MS is a simple, rapid and solvent-free method suitable for analysis of volatile compounds emitted from fresh flowers of S. oblata in different florescence.     

The application of experimental design to the robustness testing of a method for the determination of drug-related impurities by capillary electrophoresis

Summary Robustness testing of capillary electrophoresis methods is an important part of method validation. Appropriate use of experimental designs can be employed in this robustness testing. In this study experimental designs were used in the assessment of a capillary electrophoresis method used to determine drug related impurities. Initially a fractional factorial screening design was used to identify the critical parameters which were found to be pH and voltage. A central composite design was then performed to evaluate the response surfaces for pH and voltage which showed operation at the optimum pH and voltage values.     

Optimisation of a simple and reliable method based on headspace solid-phase microextraction for the determination of volatile phenols in beer

A simple, accurate and sensitive method based on headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–tandem mass spectrometry (GC–MS/MS) was developed for the analysis of 4-ethylguaiacol, 4-ethylphenol, 4-vinylguaiacol and 4-vinylphenol in beer. The effect of the presence of CO₂ in the sample on the extraction of analytes was examined. The influence on extraction efficiency of different fibre coatings, of salt addition and stirring was also evaluated. Divinylbenzene/carboxen/polydimethylsiloxane was selected as extraction fibre and was used to evaluate the influence of exposure time, extraction temperature and sample volume/total volume ratio (V_s/V_t) by means of a central composite design (CCD). The optimal conditions identified were 80 °C for extraction temperature, 55 min for extraction time and 6 mL of beer (V_s/V_t 0.30). Under optimal conditions, the proposed method showed satisfactory linearity (correlation coefficients between 0.993 and 0.999), precision (between 6.3% and 9.7%) and detection limits (lower than those previously reported for volatile phenols in beers). The method was applied successfully to the analysis of beer samples. To our knowledge, this is the first time that a HS-SPME based method has been developed to determine simultaneously these four volatile phenols in beers.     

Use of experimental design in the optimisation of stir bar sorptive extraction followed by thermal desorption for the determination of brominated flame retardants in water samples

A method for the determination of polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in water samples is proposed. The method involving stir bar sorptive extraction (SBSE) and thermal desorption followed by gas chromatography coupled with mass spectrometry was optimised using statistical design of experiments. In the first place, the influence of different polydimethylsiloxane stir bars was studied. A Plackett–Burman design was chosen to estimate the influence of five factors on the efficiency of the SBSE process: desorption time (5–10 min), desorption temperature (250–300 °C), desorption flow (50–100 mL min⁻¹), cryofocusing temperature (-130 to 40 °C) and vent pressure (0–12.8 psi). Afterwards, two central composite designs were used to find the optimal process settings that were applied to the optimisation of both desorption and extraction efficiency. In the case of the desorption parameters, long desorption times (10 min) and desorption flows lower than 70 mL min^-1 yielded the best signals for the majority of compounds. However, different behaviour among the analytes was observed for the vent pressure and we decided to fix it at an intermediate value (7 psi). In the case of extraction parameters, the sample volume and the addition of NaCl did not have a significant effect, while the addition of methanol yielded better extraction responses. Remarkable recovery (82–106%) and repeatability (less than 18%) were attained. Furthermore, excellent regression coefficients (r ² = 0.991–0.999) and low detection limits (1.1–6.0 ng L⁻¹) were also achieved for the congeners studied. The proposed method was applied to the analyses of PBDEs and PBBs in waters from the Basque Country, Spain.